Many applications and/or processes involve the unwinding of material, in the form of a web, from a roll as the material is subsequently used in the application or process. Subsequent to unwinding, the material may be used in the process and then wound onto a take-up roll, or it may be cut or slit into parts to be consumed in the process. Materials used in these processes may have widely varying physical properties, such as flexibility, breaking strength, elasticity, etc. Depending upon the physical properties of the material and/or the nature of the subsequent process, it may be important to maintain the tension in the material constant or at least within a narrow range, as the material is being unwound from the roll. As anyone skilled in the art will recognize, if the torque exerted on the roll is constant, the tension in the material will increase as it is unwound and the diameter of the roll decreases.
An example of such a process is a web type release fluid applicator for fusers in electrostatographic reproduction apparatus such as copier/duplicators, printers, or the like. In electrostatographic reproduction apparatus a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics. Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the photoconductive member. A receiver member, such as a sheet of paper, transparency, or other medium, is then brought into contact with the photoconductive member, and an electric field applied to transfer the marking particle developed image to the receiver member from the photoconductive member. After transfer, the receiver member bearing the transferred image is transported away from the photoconductive member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of fuser assembly for typical electrostatographic reproduction apparatus includes at least one heated roller, having an aluminum core and an elastomeric cover layer, and at least one pressure roller in nip relation with the heated roller. The fuser assembly rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member. Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver member.
With roller fuser assemblies, it is common practice to use release fluids, such as silicone oil for example, applied to the fuser roller surface to improve the release of image-carrying receiver members from the fuser roller. The most common types of release fluid applicators or oilers are a rotating wick roller, a donor/metering roller, an oil impregnated pad or roller, an oil impregnated web, or variations or combinations of the above. In a release oil applicator utilizing an oil-impregnated web, the web is, for example, formed as a porous membrane capable of retaining release oil. The oil-impregnated web extends from a supply roll to a take-up roll. The portion of the oil impregnated web between the supply roll and the take-up roll is directed about intermediate rollers, at least one of which is a back-up roller urging the oil-impregnated web into contact with the heated fuser roller. Another of the intermediate rollers and/or the take-up roller is driven for pulling the oil-impregnated web from the supply roll onto the take-up roll.
As explained above, if the torque applied to the supply roll is maintained constant, the tension in the oil impregnated web will increase as the diameter of the supply roll decreases due to unwinding of the oil impregnated web. As the tension increases the oil impregnated web can become distorted, thus affecting the uniformity and rate of oil delivery to the heated fuser roller. Non-uniform and variable rate of oil delivery to the heated fuser roller can cause unacceptable image quality defects in the fused marking particle image on the receiver member.